1. Field of the Invention
The present invention relates to a patterned disk medium for vertical magnetic recording, in which servo pattern areas each including a plurality of magnetic members are provided on each surface of a disk-shaped substrate. More particularly, the invention relates to a patterned disk medium for vertical magnetic recording, in which magnetic members included in servo pattern areas on each surface of a disk-shaped substrate are magnetized in a direction vertical to each surface. The invention also relates to a magnetic disk drive provided with the patterned disk medium.
2. Description of the Related Art
In general, servo information is beforehand, or at the initialization of a magnetic disk drive, recorded on a disk-shaped magnetic recording medium (disk medium) installed in the drive. Servo information includes position information necessary to position the head at a target position on the disk medium. The area recording servo information is called a servo area.
Jpn. Pat. Appln. KOKAI Publication No. 2003-22634 (prior art document 1) describes a technique related to a patterned disk medium. The patterned disk medium is a magnetic disk medium in which a servo pattern in each servo area (servo zone) is pre-provided as an irregular surface pattern formed of a magnetic layer. Prior art document 1 also discloses a so-called discrete track recording (DTR) technique for forming data tracks also using patterns, and forming grooves along the tracks. DTR is a magnetic recording technique expected to be able to improve the error rate in each data area and increase the surface recording density.
A servo pattern cannot be used as servo information if it is merely formed of an irregular pattern on a substrate with a magnetic surface layer. To realize a servo pattern usable as servo information, an initialization process for reliably magnetizing the pattern is required. Prior art document 1 discloses the following two-stage magnetization method.
Firstly, while the patterned disk medium is rotated, the magnetizing head is moved between the outer periphery and inner periphery of the disk medium. In this state, the head generates a ferromagnetic field in a first direction (first magnetic field). As a result, the magnetic layers provided on the concave and convex portions of the disk medium (i.e., the entire surface of the disk medium) are magnetized in the first direction. Subsequently, while the disk medium is again rotated, the head is again moved between the outer periphery and inner periphery of the disk medium. In this state, the head generates a magnetic field (second magnetic field) in a second direction opposite to the first direction. The second magnetic field is as weak as little influences the concave portions of the disk medium. Because of the second magnetic field, the magnetization of the magnetic layer on each convex portion of the disk medium is reversed. Thus, only the convex portions of the disk medium are magnetized in the second direction.
Another two-stage magnetization method is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-54946 (prior art document 2). The patterned disk medium described in this document employs longitudinal recording, and is a disk-shaped magnetic recording medium in which an irregular magnetic layer is formed on the surface. In the two-stage magnetization method of the prior art document 2, a magnetizing unit generates a magnetic field (first magnetic field) in a first direction, using a large direct current (DC). As a result, the magnetization of the concave and convex portions of the disk medium is adjusted to the first direction.
After that, the magnetizing unit again generates a magnetic field in a second direction opposite to the first direction, utilizing as weak DC current as little influences the concave portions. Because of the magnetic field in the second direction (second magnetic field), only the convex portions of the disk medium are magnetized in the second direction.
Yet another two-stage magnetization method is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-22056 (prior art document 3). The two-stage magnetization method described in document 3 is used for a double-sided vertical magnetic recording medium (double-sided vertical magnetic disk medium). In this method, firstly, flat magnetic layers formed on both surfaces of the disk medium are magnetized in one direction by an external magnetic field that can penetrate both magnetic layers. The surface magnetic polarity of one magnetic layer differs from that of the other layer. Subsequently, using first and second mask members, the signal patterns of these mask mediums are transferred to the magnetic layers (first and second magnetic films) provided on the respective surfaces of the disk medium. Each of the first and second mask members includes magnetic regions corresponding to the to-be-transferred signal pattern.
In the two-stage magnetization method described in prior art document 1 or 2, when the entire surface of the disk medium is magnetized in the first direction, the following problem is raised because of wide magnetic spacing. Even if a large head is used for magnetization, only a weaker magnetic field than a recording magnetic field generated by the head of the magnetic disk drive may be applied to the concave portions of the magnetic layers of the disk medium. In the two-stage magnetization method, after the entire surface of the disk medium is magnetized in the first direction, a magnetic field of a strength that does not influence the concave portions of the disk medium is generated in the second direction. However, it is not always easy to reliably reverse the magnetization of only the convex portions of the magnetic layers of the disk medium.
On the other hand, in the two-stage magnetization method described in prior art document 3, both surfaces of the double-sided vertical magnetic disk medium are magnetized by the external magnetic field that can penetrate both surfaces. In this case, a sufficient strong magnetic field can be applied to the magnetic layers on both surfaces of the magnetic disk medium, compared to prior art documents 1 and 2. However, at the second stage in the two-stage magnetization method of prior art document 3, the first and second mask members must be used to transfer their signal patterns to the magnetic layers (first and second magnetic films) on both surfaces of the magnetic disk medium.